1. Field of Invention
This invention generally relates to an improved saddle stitcher, specifically the incorporation of a signature alignment paddle into the stitcher design.
2. Prior Art
In the past ten years, printing design has become much more complicated, with intricate page designs which sometimes include continuous images which cross over from one page to the next. Designs of this type require that the individual sheets (signatures) jog up or head up, meaning that the top of all sheets are precisely aligned.
For the past 30 years, a number of methods have been employed during the printing process for signature alignment. The standard method currently used to align the signatures is with the use of a piece of spring steel attached to the stitcher. The spring steel is oriented so that it hangs down just above the signatures. It is typically bent by hand so that it lightly drags across the signatures. The intent is that this dragging action will pull the signatures against a stop and thereby align them. This method has a number of shortcomings however. Sometimes a signature rides too high on the saddle and the spring steel drags the signature off the conveyor chain, or creates a jam-up on the chain. Sometimes the spring steel pressure is too high and the steel scratches the signature. Other times the pressure is too low and the device fails to move the signature against the stop.
Another method currently used for signature alignment is the use of one or more strings mounted to the saddle stitcher. The strings are positioned in such a way as to drag along the outside of the signature as it passes. This dragging is intended to draw the signature back to a stop, where presumably it would align with a signature underneath. This method also has a number of drawbacks. First, excess drag by the string will dislodge the signature and will disrupt production. This is especially common when the signatures are textured or otherwise coated with a substance which tends to stick to the string. In addition, this method is only effective at dragging the top signature. It is not uncommon in production runs however, to have as many as six or more signatures gathered. In these cases, the string would typically only pull the top layer to the stop.
A third method is to simply place an individual along side the production line and have them manually jog each signature group to achieve the desired alignment. This method has a number of shortcomings however. First, it requires the employment of one or more individuals and adds to the cost of production. Second, manual jogging requires that the production rate be slowed to accommodate the reflexes of the average person.